Pneumatic wrenches, along with hydraulic and electric impact wrenches are one of the most used tools in a workshop, by both amateurs and professionals alike. They are used to tighten bolts to the correct torque, and loosen them, and are one of the biggest labour savers in the workshop. All styles work in the same way, by spinning a mass to a high speed and then engaging a clutch to deliver the torque in a quick burst. Of the different types, air impact wrenches are the most popular.

Many professional (and amateur) workshops use air powered tools, and of them the air impact wrench tends to get the most use. If you do any reasonable amount of work on cars, trailers, boats and the like, you'll probably benefit greatly by adding one to your own workshop. There are several choices you need to make before buying one though - specifically power source, drive size, and case/style. Let's take a look at power source first.

While air tools are the most popular, they are overkill for most home workshops. A better choice if you'll mostly be working on cars or motorcycles is a mains powered, or cordless wrench. Since you won't need a compressor and air lines, you'll be reducing your costs and that will leave more of your budget for buying quality sockets. Modern batteries and motors are both powerful and reliable, and so a cordless model would be my recommendation for most amateur mechanics since they are so convenient.

The next consideration is what size of drive and sockets you'll be needing. This will be influenced by what you'll be using the wrench for, and whether you already have some sockets. In general, the heavier the work is the larger drive you'll need. 1/2" sockets are quite suitable for working on most cards, with 1" or even 2" being needed if you'll be working on commercial or plant vehicles. Drive sizes over 2" are normally only used in heavy industrial workshops.

There is one other choice to me made, and that is style. The smallest wrenches are shaped like a screwdriver, but they are only capable of delivering low torque. Most 1/2" wrenches are of the "pistol grip" variety, shaped like an electric hand drill. As you move up to heavier duty tools you'll start to come across D and T grips which allow for a much firmer hold, and so much higher torque levels. The correct style for you will depend on the type of work you'll be doing, so take that into consideration when making a purchase.

After making your decisions for style, drive and power source you can search for a suitable model. Most of the big name brands offer a wide range of models to suit every budget, but don't ignore the budget brands. Even some of the cheaper models are quite capable, and real bargains can be had, especially if you look for discounts through online stores.